The transgenic shared resource was founded in 1988 to train and assist AECC investigators in the production and characterization of transgenic mouse strains. This technology allows analysis of gene function through the introduction of DMA sequences into the germ line, usually, although not exclusively, by pronuclear injection of fertilized oocytes. The shared resource supervisor director consults with individual investigators and advises on transgene construct, as well as making plasmids and sequence cassettes available, as well as other reagents. This results in DMA constructs suitable for expression in the mouse. Usually this is in the form of a plasmid but we also offer the injection of BAG DMA. The shared resource prepares the DNA and introduces this DNA into the oocytes by micro-injection. In some cases the sequence of interest is introduced into the oocyte by lentivirus infection. After the manipulation of the oocyte they are transferred to pseudo-pregnant mothers and following birth, the pups are cared for to weaning. At this point mice are returned to the investigator for further analysis. The production of useful transgenics usually takes less than seven weeks from submission of the DNA. We guarantee at least three founders per construct although generally more are generated. We have had essentially 100% success rate with little need for reinjection of constructs, Between 18-25 investigators use this service per year with approximately 100 constructs injected. In addition, the core provides embryo and sperm freezing for long-term storage of mouse lines, in vitro fertilization (IVF) and intra-cytoplasmic sperm injections (ICSI) to rescue frozen samples or difficult to mate strains. We also provide blastomere fusion to generate tetraploid embryos for aggregation with ES cells to determine whether the phenotypes of mutations are intrinsic to the embryo or are the result of placenta! abnormalities.